1. Field of the Invention
The present invention relates to a forming method for applying a continuous punching to a chain roller with an opening; a height of a chamfer surface of the opening is greater than 0% to 5% of the height of the opening.
2. Description of the Related Art
FIG. 8 shows a conventional forming method for applying a continuous punching to a chain roller. A raw block (a1) has a first surface (a2) and a second surface (a3). The method comprises the following steps:                A. First punching: the first surface (a2) is punched to form a first chamfering indentation (a4);        B. Second punching: the first surface (a2) is further punched to form a second chamfering indentation (a5) larger than the first chamfering indentation (a4), and the second surface (a3) is punched to form a first square indentation (a6);        C. Third punching: the second chamfering indentation (a5) of the first surface (a2) is punched to form a second square indentation (a7);        D. Fourth punching: the second square indentation (a7) of the first surface (a2) is punched to form a third square indentation (a8), and the first square indentation (a6) of the second surface (a3) is punched to form another third square indentation (a8);        E. Fifth punching: the third square indentations (a8) of the first and second surfaces (a2, a3) are individually punched to form stair indentations (a9); and        F. Sixth punching: a middle wall between the two stair indentations (a9) is propelled outside the raw block (a1) via a first blanking to form a chain roller (b) with an aperture (b1).        
Wherein, the aperture (b1) of the conventional chain roller (b) has two chamfer surfaces (b2) disposed at two ends thereof. The height of each chamfer surface is defined by 15% of the height of the aperture (b1) (as shown by the step F in FIG. 7); namely, the straight part occupies 70% of the aperture (b1).
Referring to FIG. 9 shows a speed shifting bicycle. The chain (c) is designed for allowing a speed adjustment of the bicycle, so the chain (c) would suffer for the transformation. Moreover, a chain pin bush (d) and an inner sheet (c1) of the chain (c) are integrally formed. Namely, the chain pin bush (d) is combined by two pieces of the inner sheets (c1) respectively disposed in a moiety, which further cooperate with an outer sheet (c2) to form the chain (c).
However, the conventional forming method adversely incurs the following disadvantages:                1. A distortion readily occurred: when the chain (c) sustains a large torque, the two inner sheets (c1) are easily subjected to deformation.        2. Short using life: the straight part inside the conventional chain roller (b) merely occupies 70% of the aperture (b1), so the chain roller (b) and the chain pin bush (d) have a small contact area, which readily suffers an abrasion and thence decreases the using life.        3. Bumpy speed shifting: practically, the chain (c) habitually deviates rightward or leftward, especially in time of executing the speed changing by cooperating with a gear disk. Whereby, a malposition of the chain (c) would be incurred while upward and downward switching the gear disk. As a result, the chain roller even likely derails, which brings about an inconvenient application.        